In typical pouch machines, a flat web of heat sealable material is continuously f ed from upstream of the pouch machine and is longitudinally folded upon itself by a plow or similar device. The thus-folded web is fed about a sealer which contacts the folded web along vertical heated land areas to form transverse vertical seals, and, thus, a series of open-top pouches along the web. The web of open-top pouches is passed around a filler wheel, filled with product and then sealed along the top edge of the web. The web of filled pouches then passes downstream to a motor-driven knife or rotary perforation apparatus which cuts the pouches apart or perforates the transverse vertical seal between two adjacent pouches in the web. The perforations allow the pouches to remain part of the continuous web, but facilitate the later separation from the web preferably along the perforations.
In one prior perforation apparatus, a major knife hub has a plurality of knife blades interacting with a plurality of notched knife blades of a minor hub to perforate the vertical seals between adjacent pouches in the web. More specifically, a notched knife blade on the minor hub contacts or interferes with a knife blade on the major hub to create perforations in a pattern copasetic with the notches in the knife blade. Depending on the notch configuration of the blade, the perforations are generally primitive and course, requiring special care when separating the pouches from the web along the perforations in order to avoid tearing into one of the pouches and exposing its contents. For example, when pulling such pouches apart, it is easy for a tear or crack to start at the corners of the perforations and readily extend into the unsealed pouch material, opening the pouch, rather than extending along the perforation line for pouch separation. These unwanted tears or cracks occur in part where the perforations are wide in the machine direction. To avoid unnecessary tearing into the pouches when trying to separate the pouches along the course perforations, some manufactures now avoid the perforation step completely, telling their customers to separate adjacent pouches with scissors or knife devices instead. Using scissors to separate the pouches from the web adds an extra step for the customer, making the product less desirable from a handling standpoint.
This prior perforation device has other disadvantages. For instance, because the blades must create an interference contact to create the perforations, the blades wear out quickly, greatly reducing the life of the blade. Additionally, the blades must be synchronized relatively precisely in order to properly form the perforations. For instance, if the blades are not synchronized, then the perforation may be incomplete or less desirably one of the blades may contact the pouch, tearing it open and exposing its contents. Moreover, unsynchronized blades may tear the web, requiring that the production line be stopped so that the web may be rethreaded through the perforation apparatus. The synchronization is even more difficult to achieve where there is a chord difference between the minor perforating blades on the one hub and the major hub blades on the other. The chord dimension or set-up usually varies within the ratio of about 1.0 to about 0.93 and this variation leads to tearing of the perforations during the perforation operation and undue widening of the perforation holes in the machine direction. Another difficultly experienced with prior perforating operations is the cut lengths are generally significantly larger than the secure bridges between the pouches. This severely weakens the lines of the perforation and may cause premature separation during pouch train handling.
Accordingly, one objective of this invention is to provide an improved rotary knife perforator for improving the perforation in the vertical seal between two adjacent pouches in a continuous web.
Another object of this invention is to provide an improved rotary knife perforator for creating a perforation with a refined appearance that makes separation of the pouches from the web easy and repeatable.
Another object of this invention is to provide an improved rotary knife perforator that eliminates interference contact between the blades thereby minimizing blade wear.
Still another object of this invention is to provide a non-contact rotary knife perforator that minimizes the need to synchronize respective blade edges, but still eliminates tearing of the web by the blades.